The present invention relates to antenna systems for communicating utility meter readings. In particular, but not exclusively, the present invention relates to a trident antenna arrangement associated with a utility meter, particularly a water meter, for remotely transmitting meter readings from a generally underground pit box in which the antenna is installed to a remote receiver.
In an effort to alleviate the problems associated with physically reading utility meters, utility companies have deployed remote meter transmission units. In general, a remote meter transmission unit remotely reads a utility meter and transmits the meter readings or other meter related information, directly or indirectly, back to a utility company. The remote meter transmission units transmit these meter readings, via radio frequency (RF) signals, to a central reading station or data collection unit. In some instances, the RF signal is transmitted over relatively long distances; e.g., a mile or more. Thus, a remote meter transmission unit may require a robust antenna capable of transmitting the meter readings the necessary distances.
The amount of RF energy actually irradiated into the air, as compared with the potential energy that could be radiated is based on a number of factors. These include applied voltage, the amount of current flowing through the antenna, the frequency of the rf signal applied to the antenna, the material from which the antenna is made, the antenna's geometry, and those materials in surrounding space relatively close to the antenna (e.g., a sphere-radius of up to a few wavelengths of the rf signal applied to the antenna). When the space surrounding an antenna varies, the antenna's performance (i.e., the amount of energy radiated therefrom) will correspondingly vary.
Various factors to be considered in designing and implementing an integrated antenna system include, without limitation:
frequency of operation;
transmitter output power;
antenna gain, polarization, characteristic impedance, geometry, and radiation pattern;
azimuth beam-width and variation;
coefficient of maximum wave reflection;
location where the antenna will be installed;
ability to effect antenna installation;
desired length of service;
ability to operate in exposed environmental conditions (such as exposure to water) with only very small variations in operation performance (due to any water absorption into the antenna system);
resistance to ultra-violet light;
shock and vibration resistance;
environmental temperature variability resistance; and,
government regulations for operating radio equipment.
At the same time, the utility must be aware of cost factors and the ability to manufacture a large volume of such units (for use in a full system having a number of meter reading locations) that are reliable and exhibit repeatability of performance.